Other versions exist on this site from various publications. This one is from the Radio Electronics Experimenter from 1990. The bargraph circuit uses the UAA170.
In the figure we have the typical configuration of a sinusoidal audio oscillator with twin-T. The...
This circuit that uses only common transistors can operate between 60 and 130 MHz, depending on...
This RCA / GE circuit from the 90s can be applied to any modern operational amplifier. The number...